Hydrogen may be used as a fuel for fuel cells, internal combustion engines and other hydrogen-consuming systems. All hydrogen powered devices require a mechanism for supplying hydrogen. Hydrogen may be supplied from a suitable on-board hydrogen store. A device which has a local hydrogen supply coupled with a suitable mechanism for delivering hydrogen from the supply to the hydrogen consuming part of the device may be made to be mobile. Examples include fuel cell or internal combustion powered vehicles, or fuel cell powered portable electronic devices.
The prevailing paradigm for designing hydrogen powered systems is to implement a scheme of periodically refilling the on-board storage in a manner analogous to the way gasoline is used to refuel conventional internal combustion engines. In portable devices the refueling can be done by refilling an on-board tank, or by using a removable, replaceable, tank so that refueling the device becomes analogous to replacing primary batteries in a conventional battery-powered portable electronic device. In either case, fuel is delivered to the device, stored on-board, and then delivered into the fuel cell or other hydrogen-consuming part of the device.
A conceptual schematic block diagram of these prior art configurations is shown in FIG. 1A. Fuel 10 is placed into a fuel tank 20 that is connected to an energy converter 30 (e.g. a fuel cell) through a delivery mechanism 40.
In FIG. 1B a fuel 10 is provided in a removable fuel cartridge 20A that is connected to energy converter 30 through delivery mechanism 40A.
The low volumetric energy density of hydrogen gas presents problems in designing practical hydrogen-powered devices. While hydrogen has the highest energy density of any known substance by weight, its volumetric energy density is quite low. In order to make hydrogen-powered devices feasible some means of storing hydrogen that improves its volumetric energy density must be provided.
For hydrogen power to compete effectively with conventional gasoline or battery power the volumetric energy density of the stored hydrogen must be increased. Typical targets for volumetric energy density are described in M. Conte et al. Overview of energy/hydrogen storage: state-of-the-art of the technologies and prospects for nanomaterials, Materials Science and Engineering B, vol. 108, Issue 1-2, April 2004, pp. 2-8, which is hereby incorporated herein by reference. The US Department of Energy goal for hydrogen storage is to achieve >63 kg/m3 hydrogen by volume, and >5% hydrogen by weight.
In prior art systems, fuel tanks or fuel cartridges and fuel delivery mechanisms must be designed to interface between the characteristics of the fuel and the requirements of the device being supplied by fuel. For example, hydrogen fuel cells require a supply of hydrogen in which the purity, temperature, humidity, pressure and flow rate of the hydrogen are typically required to be controlled. Any means for connecting a fuel supply (tank or cartridge) to a fuel cell system must ensure the characteristics of the hydrogen entering the fuel cell are compatible with these requirements. A central problem in the design of fuel cell systems is that the characteristics of the fuel required by the fuel cell are typically very different from the characteristics of high energy density hydrogen storage. Fuel delivery mechanisms 40, 40A must be carefully designed to receive hydrogen under the conditions of the hydrogen tank or cartridge and to supply hydrogen in a state required by a fuel cell. This is a central function in most fuel cell systems, leading to significant complexity in design and manufacture.
Compressing hydrogen to very high pressures increases the density of the stored gas. Small compressed gas cylinders can safely store hydrogen at up to 700 bar in composite structures that achieve energy densities approaching 6% by weight. Even these are still quite large on a volumetric basis. Few, if any, fuel cells can withstand such high pressures. The interface between such a high-pressure storage canister and a fuel cell must provide valving, step-down pressure regulators and flow controllers suitable to provide the hydrogen to the fuel cell at a pressure and flow rate appropriate to the fuel cell. Regulators, in particular, are a problem since typical fuel cell systems operate at pressures less than 4 bar. Achieving a step-down pressure regulation of 150 times or more can be difficult.
The following are some example high pressure hydrogen storage systems:                U.S. Pat. No. 6,651,307 “Process for manufacturing a pre-stressed fiber-reinforced high pressure vessel”;        U.S. Pat. No. 6,676,163 “Replaceable fuel system module and method”;        U.S. Pat. No. 6,634,321 “Systems and method for storing hydrogen”; and,        U.S. Pat. No. 6,755,225 “Transportable hydrogen refueling station”.        
Liquified hydrogen can be stored in highly insulated dewars. Liquefied hydrogen has energy densities approaching the requirements for transportation applications. There are difficulties in managing the boil off of hydrogen that occurs if the liquid is left unused for prolonged periods. Further, when hydrogen is needed to operate the fuel cell, a conversion from liquid to gaseous hydrogen must be effected almost instantaneously. Therefore the delivery mechanism must at once super-insulate but then rapidly boil the liquid hydrogen in an efficient controlled and regulated fashion.
Various hydrogen-generating chemical compounds, known as chemical hydrides, can be used as a ‘fuel’ from which hydrogen can be generated locally. Systems which use such fuels must include a ‘hydrogen generator’ component before the hydrogen delivery mechanism. A system having a hydrogen generator 50 is shown in FIG. 2. A central challenge in designing a practical hydrogen generator is to provide a practical mechanism for controlling the rate of conversion of the chemical hydride to hydrogen and by-products to roughly match the rate at which hydrogen is demanded by the system.
Examples of rate-controlling hydrogen generators include:                CA 2,373,553, “Ca, Mg, and Ni Containing Alloys and Method for Preparing & Use Thereof for Gas Phase H2 Storage”; and,        CA 2,406,603, “Method of H2 Generation for Fuel Cell Applications and H2 Generation System”.        
There are a large number of hydrogen-containing chemical compounds which have hydrogen storage characteristics that are extremely attractive for mobile hydrogen energy systems. Some such compounds are listed in Table I. Controlling the rate at which hydrogen is produced from these compounds is very difficult. This lack of control makes such reactions unsuitable for directly supplying hydrogen to a fuel cell or other hydrogen-consuming device.
TABLE ISome Hydrogen-Producing ReactionsVolumetric H2 DensityWeight(ml reactant/liter of H2ReactantsProducts% H2released @ STP)Comments2Al + 6H2O3H2 + 2Al(OH)3~3.51.81Needs causticwater solutionNaH + H2OH2 + NaOH4.81.56CaH2 + 2H2O2H2 + Ca(OH)25.21.35MgH2 + 2H2O2H2 + Mg(OH)26.51.2Mg(AlH4)2 + 8H2O8H2 + Mg(Al(OH)4)27.0N/AMg(AlH4)2 notreadily availableAlH3 + 3H2O3H2 + Al(OH)37.2N/ALiAlH4 + 4H2O4H2 + LiAl(OH)47.31.27NaBH4 + 4H2O4H2 + NaB(OH)27.31.2Requires catalystLiH + H2OH2 + LiOH7.71.16LiBH4 + 4H2O4H2 + LiB(OH)28.61.16N2H42H2 + N212.50.71Requires catalyst0.85Mg(BH4)2 *99.8% pure H212.84N/ARequires source2NH3 + 0.075Liof ignitionNO3 + 0.075PTFENH4F + LiBH44H2 + BN + LiF13.60.78Requires sourceof ignitionN2H4 + 2NH35H2 + 2N215.10.74Requires pressurevessel and catalyst0.5NH3BH3 +94% pure H216.52N/ARequires source0.3N2H4 * 2BH3 +of ignition0.098(NH4)2B10H10 + 0.102NH4NO3700 Bar H2H21001.43Requires highpressure vessel
Prior art approaches to fueling hydrogen powered devices typically share the characteristics of bringing high energy density hydrogen carriers (hydrogen fuels) on-board the device and of implementing a specialized mechanism to convert the stored hydrogen fuel to hydrogen. As a result, such hydrogen powered systems are limited in the range of ‘fuels’ that can be employed. Only fuels for which a rate controlling delivery mechanism can be designed are feasible, and each hydrogen-powered system must be tuned to operate from one and only one type of hydrogen fuel. These two characteristics present an impediment to the design and deployment of practical hydrogen-powered systems.
There remains a need for practical methods and apparatus for supplying hydrogen to hydrogen-fueled devices.